1. Field of the Invention
The invention relates to a core that constitutes a reactor mounted on a hybrid vehicle or a fuel cell vehicle.
2. Description of the Related Art
Vehicles in which a driving force is produced by a motor, such as hybrid vehicles, electric vehicles, and fuel cell vehicles, have been drawing much attention as environmentally friendly vehicles. Generally, in such vehicles, direct-current voltage supplied from a secondary battery is converted into alternating-current voltage using an inverter and the alternating-current voltage is applied to a three-phase alternating current motor. In this process, a boost converter is used to boost the direct-current voltage supplied from the secondary battery before supplying this direct-current voltage to the inverter.
The boost converter may include a reactor having a core and a switching element. A core 10 in FIG. 3 is an example of existing cores. The core 10 includes two end core members 12, each of which is substantially U-shaped, and a plurality of substantially quadrangular prism-shaped intermediate core members 14. The intermediate core members 14 are adhesively-fixed to each other and linearly aligned between the ends of one of the end core members 12 and the ends of the other core members 12. In the core formed of the end core members 12 and the intermediate core members 14, gap plates 16 made of, for example, ceramic, are interposed between bonding faces of the core members in order to produce magnetic gap to avoid degradation of inductance.
As the core members 12 and 14 of the reactor, compressed powder magnetic cores that are produced as follows may be used. Soft magnetic powder of which the face is insulation-treated is mixed with a binder when necessary, and then the mixture is press-molded under a predetermined high pressure. Then, the press-molded mixture is sintered or thermally treated when necessary. Each core member has bonding faces to which adjacent core members are bonded when the core 10 is assembled. The bonding faces of the core member formed of the thus produced compressed powder magnetic core may be formed not into flat faces but into convexly curved side faces that convexly bulge outward slightly, due to, for example, residual inner stress caused during the press-molding process or thermal expansion caused during the sintering process.
Japanese Patent Application Publication No. 2006-135018 (JP-A-2006-135018) describes a technology for improving bond performance to avoid bond separation between a core member and a spacer 40. According to JP-A-2006-135018, as shown in FIG. 4, projections 44a and 44b that contact the core member are formed on a bonding face 42 of the spacer 40 to which the core member is bonded, whereby the amount of adhesive applied between the spacer 40 and the core member is increased. In this way, separation between the core member and the spacer is less likely to occur.
However, as shown in FIG. 5, if the spacer 40 described in JP-A-2006-135018 is provided between the core members 14 that have curved bonding faces 15, the projections 44b formed near the outer edges of the spacer 40 do not contact the core member 14, and only the projection 44a formed at the center of the spacer 40 contacts the curved bonding face 15. In this state, the core members 14 are adhesively-fixed to each other with an adhesive 24. In this case, linear alignment and configuration of the core members 14 along a direction X (shown in FIG. 3) between the end core members 12 is not ensured, and inclination or misalignment of the core members 14 in a direction Y and/or a direction Z tends to occur.
If the core 10 with the inclined core members 14 is fixed in a reactor case via brackets that support the end core members 12, stress concentration occurs in the adhesive 24 present between the core members 14 that are adhesively-fixed to each other and that are inclined, and bond separation is likely to occur at a portion in which the stress concentration occurs due to vibration or a temperature change during the operation of the reactor. This bond separation between the core members 14 may cause degradation of noise-vibration performance of the reactor.